Chinese Carbon Tool Steel Grades T7 to T13, Hardening and Tempering
The T series is the Chinese plain carbon tool steel family, and it is the group that answers to AISI W1 on a European or American drawing. The grades run from T7 at 0.65 percent carbon to T13 at 1.35 percent, and what separates them is carbon content alone. This page collects the published composition, the recommended hardening temperature and the hardness each grade holds after tempering, so a tool shop can pick the carbon level that matches the job and set the furnace from one sheet.
Reference only. The figures below are a reference summary of published Chinese handbooks and standards practice, not an Aobo Steel specification. Confirm the grade and the heat treatment against the mill certificate and the governing drawing before an order or a production run is set against them.
What the T series is
T7 to T13 are water hardening grades. They are simple carbon steels with no deliberate alloy addition beyond the silicon and manganese left from deoxidation, so they are cheap, easy to forge and easy to grind, but they harden only in thin sections and they distort more than an alloy tool steel. The carbon range is the whole design variable. T7 and T8 are the tough end of the series, T10 and T11 balance hardness with a usable core, and T12 and T13 are the high carbon end where wear resistance is bought at the cost of toughness. All of them are tempered at low temperature, in the 140 to 250 degrees Celsius band, and above 250 degrees the hardness falls away quickly, which is the behaviour the tempering table below records.
Chemical composition
The seven grades differ in carbon only. Silicon, manganese, phosphorus and sulfur are held to the same limits across the whole series, which is why a heat treater can treat them as one family and simply follow the carbon number when setting the austenitizing temperature.
| Grade | C | Si | Mn | P | S |
|---|---|---|---|---|---|
| T7 | 0.65 to 0.74 | 0.35 max | 0.40 max | 0.035 max | 0.030 max |
| T8 | 0.75 to 0.84 | 0.35 max | 0.40 max | 0.035 max | 0.030 max |
| T9 | 0.85 to 0.94 | 0.35 max | 0.40 max | 0.035 max | 0.030 max |
| T10 | 0.95 to 1.04 | 0.35 max | 0.40 max | 0.035 max | 0.030 max |
| T11 | 1.05 to 1.14 | 0.35 max | 0.40 max | 0.035 max | 0.030 max |
| T12 | 1.15 to 1.24 | 0.35 max | 0.40 max | 0.035 max | 0.030 max |
| T13 | 1.25 to 1.35 | 0.35 max | 0.40 max | 0.035 max | 0.030 max |
Source, published Chinese tool steel data, Table 4-1 (common cold work die steels) and Table 4-64 (T13), printed pages 92 and 96. Values are mass percent.
Recommended hardening temperature
Two quench routes are published for every grade. The first is the fast route, water or a 5 percent brine or a 5 to 10 percent caustic solution, which is used where full through hardening is wanted and the section is small. The second is a slower oil or hot bath route, molten nitrate or a caustic bath held at 150 to 200 degrees Celsius, which is used for thin parts and for shapes that would crack in a plain water quench. The austenitizing window shifts down as carbon rises, from 800 to 830 degrees Celsius at T7 to 750 to 800 at T8 and back up to about 770 to 790 from T9 onwards, so the temperature cannot be carried over from one grade to the next without checking.
| Grade | Water, brine or caustic quench, °C | Hardness HRC | Oil or hot bath quench, °C | Hardness HRC |
|---|---|---|---|---|
| T7 | 800 to 830 | 61 to 63 | 810 to 840 | 60 to 63 |
| T8 | 750 to 800 | 62 to 64 | 800 to 820 | 60 to 63 |
| T9 | 770 to 790 | 62 to 64 | 790 to 810 | 62 to 64 |
| T10 | 770 to 790 | 62 to 64 | 790 to 810 | 62 to 64 |
| T11 | 770 to 790 | 62 to 64 | 790 to 810 | 62 to 64 |
| T12 | 770 to 790 | 62 to 64 | 790 to 810 | 62 to 64 |
| T13 | 770 to 790 | 62 to 64 | 790 to 810 | 62 to 64 |
Source, published Chinese tool steel data, Tables 4-9, 4-20, 4-27, 4-38, 4-48, 4-60 and 4-68, printed pages 97 to 111. The brine variant of the fast route is published at 62 to 65 HRC for T8 to T13.
Hardness after tempering
Tempering is short and low, two hours in the 140 to 250 degrees Celsius band for stress relief and dimensional stability, or higher where hardness has to be traded away. The table holds the hardness each grade leaves at a set of tempering temperatures, which is the read a shop needs when an application calls for something softer than the as-quenched figure.
| Grade | 100 °C | 150 °C | 200 °C | 250 °C | 300 °C | 350 °C | 400 °C | 450 °C | 500 °C | 550 °C | 600 °C |
|---|---|---|---|---|---|---|---|---|---|---|---|
| T7 | 62 | – | 60 | – | 51.5 | – | 43 | – | 33 | 28 | 22 |
| T8 | 62 | 60.5 | 60 | – | 53 | – | 44 | – | 38 | 31 | 27 |
| T9 | 62 | 61 | 60 | – | 55 | – | 46 | – | 36 | 31 | 27 |
| T10 | 63 | 62 | 61 | 58 | 54 | 50.5 | 47 | – | 38.5 | – | 28 |
| T11 | – | 62.5 | 61 | 58 | 54 | 50.5 | 47 | – | 38.5 | – | 28 |
| T12 | 64 | 62.5 | 60 | 58 | 54 | 50 | 48 | 44 | 38 | – | – |
| T13 | 64 | – | 60 | – | 54 | – | 48 | 44 | 38 | – | – |
Source, published Chinese tool steel data, Tables 4-11, 4-22, 4-29, 4-41, 4-51, 4-62 and 4-71, printed pages 97 to 113. Hardness in HRC after a two hour temper. A dash marks a temperature that the source does not publish for that grade, not a missing value.
How the carbon level decides the use
At the low carbon end T7 and T8 are used for tools that see impact, such as chisels, punches, shear blades and simple blanking dies, where the lower carbon buys toughness and the hardness ceiling of about 62 HRC is accepted. T9 and T10 are the general purpose middle of the series, used for taps, reamers, woodworking cutters, cold heading punches and small forming dies, with T10 being the grade most often specified when a drawing calls out a plain carbon tool steel without naming a number. T11, T12 and T13 are the high carbon end, used for turning and milling cutters, broaches, thread cutting tools and small punching dies where edge wear rather than shock sets the life. The same logic runs through the whole family, and it is the reason a shop can hold one hardening procedure and one tempering chart for all seven grades.
Because these grades harden only in thin sections, they are rarely the right answer for a large die block. That role belongs to the alloy cold work steels, and a grade such as D2 or O1 is specified instead when the section is heavy or the distortion has to be controlled. Use the T series where the carbon tool steel is the intentional choice, and move up to the alloy grades when the drawing calls for through hardening in a large section.
Notes on the data
The composition figures are published as GB/T 1298 ranges for the plain T grades and higher phosphorus and sulfur limits apply to the A suffix grades, which are the controlled quality variants T12A and T13A. Those variants are not listed separately here because they share the same carbon range and the same heat treatment as the parent grade.
The hardening and tempering tables carry only the figures the source publishes for each grade. T7, T11 and T13 do not have every 50 degree tempering point listed, and the dash in those cells records that fact rather than an omission from the transcription. The multi-stage quench media named in the source, molten nitrate and caustic baths, are recorded here as a single hot bath route because the published hardness outcome is the same across that scheme group.
The source also prints a sub-zero treatment for T10, T11 and T12 at minus 50 degrees Celsius, held within one hour of quenching, which adds one to two HRC and is used for dimensional stability on precision dies. It is mentioned rather than tabulated because the source notes that for plain carbon tool steel the economic return is low.
Compiled from a Chinese mould and tool steel heat treatment handbook, Tables 4-1, 4-9 to 4-11, 4-20 to 4-22, 4-27 to 4-29, 4-38 to 4-41, 4-48 to 4-51, 4-60 to 4-62, 4-64 and 4-68 to 4-71, printed pages 92 to 113. Every figure was read from the searchable text layer of the source file. The tables are a reference summary of published Chinese practice rather than an Aobo Steel specification, so confirm the grade and the heat treatment condition with the mill certificate before an order is placed against it.